Shaft and like oil seals

ABSTRACT

A shaft seal having a lip of an elastomeric sealing ring formed with a frusto-conical band around the shaft and has an annular non-constant clearance around the shaft and wherein upon shaft rotation liquid pulsation in said clearance causes oscillation of the band which in turn causes displacement pumping towards the oil side of the shaft.

This invention relates to shaft and like oil seals, for preventingliquid leakage between relatively rotatable members, such as a rotaryshaft and its housing.

Usually the liquid to be sealed is lubricating oil, the seals thereforecommonly being called "oil seals", the side of a seal to be installedfacing towards the region to be sealed being called the "oil side" andthe other side being called the "air side" because it is usually open toatmospheric pressure.

Shaft seals are usually mounted fluid tight fast in a shaft housing andhave an inner peripheral lip to seal around a cylindrical surface of arotary shaft. Such seals are known as "internal seals". Occasionallyhowever shaft seals are designed to be mounted fluid tight on a rotaryshaft to seal by an outer peripheral lip against a surroundingcylindrical surface of a housing and are then called "external seals".In general, the design and operating conditions of internal seals can,by simple inversion, be applied to external seals. Consequently,references in this specification to internal seals are to be treated asapplicable to external seals, unless otherwise stated.

Usually the sealing lip or ring of a shaft seal is made of a resilientlydeformable material, such as an oil-resistant synthetic rubber orelastomer.

During the last twenty years, "positive action" seals have beendeveloped and these have helical ribs, or similar configurations, at theair side of the sealing or contact band of a sealing lip or ring for thepurpose of returning leakage oil towards the oil side.

There have been proposals to provide ribs or other configurations at theoil side of a sealing or contact band of a sealing lip or ring but, sofar as is known, these have not come into use and whether any positiveaction is achieved thereby has not been established.

The present invention provides a positive action oil seal which utilisesrelative rotation of sealed members to generate at a sealing contactband a pumping action to displace oil towards the oil side.

According to the invention, there is provided an oil seal to opposeleakage of oil from between relatively rotatable coaxial members, one ofthe relatively rotatable members having a sealed circularcounter-surface of given diameter; the oil seal having an oil side andan air side and comprising: an elastomeric sealing member; a circularsealing contact band formed on said elastomeric sealing member andarranged to bear against the circular countersurface; said contact bandbeing designed to diverge from the counter-surface, to define with thecounter-surface an annular sealing region which enlarges incross-sectional area toward the oil side of the seal; and a skirtprovided at the oil side of said elastomeric sealing member, said skirtbeing constructed and arranged to have a continuous but non-constantannular clearance from said counter-surface and so as to be oscillatableby pulsations in the adjacent oil; the construction and arrangementbeing such that relative rotation between the counter-surface and saidelastomeric sealing member produces pulsations in oil filling theannular clearance, the oil pulsations cause the contact band to osculateagainst the counter surface over at least part of said annular sealingregion and the contact band osculations produce displacement pumping ofoil from the annular sealing region toward the oil side of the seal.

The term "contact" is of course used to include nominal or effectivecontact, with an interposed oil film, to maintain a meniscus between thecontact band and its counter-surface, as well understood in oil sealtechnology.

The osculation of the contact band against its counter-surface maycomprise either or both deformation, of the elastomeric material of thesealing member, or oscillation of the contact band eccentrically to thecounter-surface, thus varying cyclically the radial dimension of theannular sealing region to produce a pulsating pumping action towards theoil side.

The non-constant clearance of the skirt from the sealed member, usuallya sealed shaft surface, can be achieved in a variety of ways, includingeccentricity or a lobed configuration of the skirt. It could be achievedby shaping of the shaft or other sealed surface but this is not reallypracticable having regard to the practice of providing shaft seals tofit any shaft of a given diameter and surface finish.

The invention is illustrated by way of example on the accompanyingdrawings, in which:

FIG. 1 is a somewhat diagrammatic axial section of an internal lip shaftseal in place on a shaft, the proportions of the seal being exaggeratedto illustrate on a relatively large scale the seal and shaft contactzone.

FIGS. 2, 3 and 4 are fragmentary axial sections, on a much enlargedscale, illustrating one mode of displacement pumping action, byresilient deformation of the seal of FIG. 1, and

FIG. 5 is a fragmentary axial section, on a very much enlarged scale, toillustrate eccentric oscillation of the contact band to produce anothermode of displacement pumping action of the seal of FIG. 1

The internal lip shaft seal shown by FIG. 1 is basically of a well-knownconstruction with a metal case 1 of L-section of which the axial flange2 fits fluid-tight in a surrounding shaft housing (not shown) and theradial flange 3 has bonded to its inner-peripheral rim a syntheticrubber sealing ring 4 moulded on to the case.

The sealing ring 4 has a sealing head 5 with a circumferential groove 6in which is seated a constricting garter spring 7 which loads thesealing head 5 resiliently to contact the cylindrical surface of a shaft8 by a lip 9.

As so far described, the seal of FIG. 1 is conventional. The oil side ofthe seal is indicated as O and the air side as A.

In accordance with the present invention, the lip 9 has its innerperiphery formed as a frusto-conical contact band 10 around the shaft 8(see FIG. 2) and a skirt 11, in the form of a tapered axial flange isprovided on the sealing head 5 at the oil side O.

As best shown by FIG. 2, the frusto-conical contact band 10 is designedto make constant close contact, with a shaft of given diameter, by theedge 12 at the air side A of the flange 9 and to diverge from the shaftsurface to define a sealing region 13 which enlarges in cross-sectionalarea towards the oil side O.

Instead of the contact band 10 being moulded frustoconical, it could becylindrical and be constricted to frusto-conical shape by the assymetricload of the garter spring 7. A moulded frusto-conical surface is howeverpreferred as being more definite.

The skirt 11 has an annular clearance 14 around the shaft and, in oneway or another, this clearance is designed to be non-constant so that,when the shaft 8 rotates, pulsation of oil is produced, in the clearance14, to oscillate the skirt, thus cause osculation of the contact band 10against the opposed shaft surface and thereby displacement pumping ofoil in the sealing region 13 towards the oil side O.

This pumping action is illustrated in a very simple manner by FIGS. 3and 4 which represent a single cycle of the skirt 11 deflecting to archthe contact band 10 away from the shaft (FIG. 3) and then reversing tocause the contact band to approach and "kiss" the shaft (FIG. 4) andthus displace oil towards the oil side and away from the contact edge 12which is the boundary for leakage. This cycle takes place at shaftrotational speed or higher.

Another mode of pumping action is illustrated by FIG. 5 which shows thecontact band 10 displaced slightly radially, so that it is eccentric tothe shaft, with a consequent cyclic variation in the radial dimension ofthe sealing region due to the pulsating action of the skirt. The radialvariation should not be so great as to break down the sealed liquidmeniscus M at the edge 12.

It is considered probable that the osculation of the contact bandagainst the shaft surface in practice is a complex combination of atleast the two modes of pumping action illustrated. Every shaft has someeccentricity, of shape or rotation however slight, and this is a factorwhich affects the radial dimension of the sealing region, apart from theeffect of the oscillation of the skirt in the present invention.

It will be appreciated that the above description is only a verysimplistic explanation of the positive action pumping effect ofproviding a seal with a contact band diverging from the shaft surfacetowards the oil side and a skirt with a non-constant clearance aroundthe shaft. The improved sealing performance of such a seal can bedemonstrated, such as by a back-to-back test against a conventionalseal, but a closer theoretical explanation, of what must be a verycomplex effect at the seal-shaft interface, cannot at present beoffered.

Possible ways of providing for a non-constant clearance 14, between theskirt 11 and the shaft surface, include moulding the skirt slightlyeccentric to the seal axis, so that the dimensions R¹ and R² in FIG. 1are different and the radial dimension of the clearance 14 progressivelyvaries around the shaft.

Another way, illustrated in FIG. 2, is to mould the inner surface of theskirt 11 with an arcuate boss or lobe 15 so that oil entrained withshaft surface rotation has a path of varying radial dimension around theclearance 14 and this will set up oscillation of the skirt. The shapeand extent of the lobe 15 as illustrated is only for example. Theradial, circumferential and axial dimensions of such lobes may beselected to suit requirements.

The conical angle of the contact band will be selected in accordancewith other factors affecting the oil displacement, or hydrodynamic lift,of the contact band. Such factors include the dimensions and material ofthe sealing ring, the shaft speed and other operating conditions,including the fluid viscosity and other fluid characteristics, for whichthe seal is designed. Present indications are that a small angle, of5°-10°, will be effective.

I claim:
 1. An oil seal to oppose leakage of oil from between relativelyrotatable coaxial members, one of the relatively rotatable membershaving a sealed circular counter-surface of given diameter; the oil sealhaving an oil side and an air side and comprising: an elastomericsealing member; a circular sealing contact band formed on saidelastomeric sealing member and arranged to bear against the circularcounter-surface; said contact band being designed to diverge from thecounter-surface, to define with the counter-surface an annular sealingregion which enlarges in cross-sectional area toward the oil side of theseal; and a skirt provided at the oil side of said elastomeric sealingmember, said skirt being constructed and arranged to have a continuousbut non-constant annular clearance from said counter-surface and so asto be oscillatable by pulsations in the adjacent oil; the constructionand arrangement being such that relative rotation between thecounter-surface and said elastomeric sealing member produces pulsationsin oil filling the annular clearance, the oil pulsations cause thecontact band to osculate against the counter surface over at least partof said annular sealing region and the contact band osculations producedisplacement pumping of oil from the annular sealing region toward theoil side of the seal.
 2. An oil seal as claimed in claim 1 wherein saidskirt on the elastomeric sealing member is arranged to be eccentric withrespect to the rotational axis of the relatively rotatable members,thereby to provide said non-constant annular clearance from the countersurface.
 3. An oil seal as defined in claim 1 wherein said skirt on theelastomeric sealing member is provided with lobes extending toward thecounter-surface, thereby to provide said non-constant annular clearancefrom the counter-surface.
 4. An oil seal as claimed in claim 1 whereinsaid skirt is formed as a tapered axial flange axially adjacent saidcontact band, and the skirt is so contructed and arranged that at leastpart of its annular clearance from the countersurface is greater thanthe annular clearance of the divergent contact band.
 5. An oil seal asclaimed in claim 4 wherein all of the annular clearance of said skirt isgreater than the maximum annular clearance of said contact band.
 6. Anoil seal as claimed in claim 1 wherein said contact band is of generallyfrusto-conical section with a conical angle of about 5°-10°.